High temperature fan



5:. NYGR EN HIGH TEMPERATURE FAN Filed May 22, 1944 8 s heets sheei 1 v Oct. 2, 1945, QNY REN 2,3 5,337

HIGH TEMPERATURE FAN Fiied ma 22, 1944' "a Sheets-Sheet 2 [.9 3i 3]" 30 2 v v I I INVENTOR. I Kari /Vy re]? aim r Ogt. 2,1945. CQNYGREN 7 ,8

.HIGH TEMPERATURE FAN 7 Filed May 22, 1944 a Sheets-$heet 4 INVENICR.

I c. NYGRENV 2,385,837

Oct. 2,1945. A

HIGH TEMPERATURE FAN Filed May 22', 1944 a Sheets-Sheet 5 in 7x 4: 50

(but. 2, 1945. c. NYGREN I 2,385,837

HIGH TEMPERATURE FAN Filed May- 22, 1944 a Sheets-Sheet e Oct. 2, 1945. c. N'YGREN HIGH TEMPERATURE FAN Filed May- 22, 1944 8 Sheets-Sheet 7 Get. 2, 1945. c. NYGREN HIGH .IEMPERA'TURE FAN Filed May 22, 1944 e Sheets-Sheet a r INVENTOR.

Patented Oct. 2, 1945 men 'rmurnaa'rnan ran Michigan City,

Ind.. assignor to Michiana Products Corporation, Michigan City, 1 'Iud., a corporation of Indiana Application May 22, 1944, Serial No. 536,801

20 Claims. (craze-209) The invention relates to-centrifugal fans orblowers for heat treating furnaces and the like. and has for its principal object to provide a simple construction that will allow appropriate freedom of movement among the parts in expanding and in contracting while maintaining the necessary relationship in the whole for-dynamic balance in use. Generally speaking, this is accomplished by making the blades carry the shrouds interlocked with their side edges,for functional operation together but with freedom of relative movement in expanding. making the inner end and contracting and portions of the blades fast Fig. 12 15a perspective .view of one of the blades in the preferred form of construction; I

Fig. 13 is a fragment of one of the shrouds; Fig. 14 is a sectional view corresponding to Fig. 9, of a single inlet fan-of the preferred construction; 1

Fig. 15 is 9.

blades of a single inlet fan shown in Fig. 14;

to their hub or to their shaft for driving and to prevent outward bodilymovement under centrifugal force.

Two double inlet fans and two single inlet fans are shown in the accompanying drawings. Figs. 1 to 8, and the corresponding description are taken from my application, Serial No. 450,847, filed July 14, 1942, of which the present application is a continuation in part. The remaining figures, Nos. 9 to 22, and the corresponding description disclose thepreferred construction embodying improvements made in the course of further research and experience with the earlier construction in .actual service.

In the accompanying drawings:

Figs. 1 and 2 are diagrammatic views of a double inlet fan and its associated parts in one form of installation; 7 1

Fig. 3 is a longitudinal sectional view through a fan and hollow fan shaft taken on the line Fig. 4 is a perspective view of one of the hub portions for securing the blades together and to the shaft, as shown in Fig. 3;

Fig. 5 is a section Fig. 3, with parts of one of the shrouds and some of the blades broken away to reveal the construction and assembly;

Fig. 6 is a perspective view of one of the blades,

Fig. 7 is a section similar to Fig. 3, of a single inlet fan,

Fig. 8 is a perspective view of one of the blades of a single inletfan;

Fig. 9 is a longitudinal sectional view through a fan and hollow shaft of the preferred construc-- tion and corresponding to Fig. 3; v i

Fig. 10 is a perspective view of one of the hub portions for securing the blades together and to the shaft, as shown in Fig. 9; Fig. 11 is a part side elevation and part section taken on the line I l-.il of Fig. 9;

taken on the line 5-4 of Fig. 16 is a fragment of the shroud at the left in Fig. 14;

Fig. 1'7 is a frame in Fig. 14; l

Figs.I18 and 19 are'fragmentary sectional views corresponding to a portion of Figs. 9 and 14, and showing a different means of positively fastening the bladesto the hubs or interlocking them with the hubs; Fig. 20 is a fragment of a blade corresponding to Figs. 18 and 19; I

Fig. 21 is a fragmentary view corresponding to Figs. 18 and 19, showing a further modified t of the shroud at the right form; and.

shaft ll, journaled in Fig. 22 is a fragment of a blade corresponding to that modified form.

' But these particular forms. and the corresponding description are used for the purpose of. disclosure' only and necessary limitations In Figs. 1 and 2,

on the claims. 1 l0 indicates a conventional form of masonry installation for a fan or blower within which is the metal casing Ii for a double inlet fan l2 mounted on a hollow water-cooled bearings ll and driven by a motor l5 through V-belt drive It. The inlet side of a water-cooling unit is shown generally at H, and the return side is shown generally at l8.

Water cooling is ordinarily used in fan constructions' for propelling high temperature fluids euch as the gases circulated in heat treating furionace 0 inner-end is integral The detail of the double inlet fan is shown in Figs.'3, 4, 5 and 6, Sheets 2 and 3. The fan is composed of twelve blades 18, two circular shrouds 20, and two hub portions on the hollow shaft 13.

From the perspective view in Fig. 6 it will be seen that the fan blades in this instance are each composed of a generally rectangular flat plate having the inner corners cut away at 12 and the with a sector shaped base 23, the assembled inner surfaces 24 of which conform to the cylindrical surface of the shaft 13. Adjacent to its base 23 each blade is thickened to form the flllerpiecesor machining pads 25. y at or adjacent to each edge, each blade is perspective view of one of, the

are not intended to impose un- 2|. assembled with the tapered ends thickened and provided-with grooves 26 whereby at each side of each groove there appear ribs 21 and 28. I

Each shroud 20 is a Wardly opening slots formed onthe enlarged portions 36, which straddle the corersponding blades.

The left hub 2| rests against a shoulderv 35 (Fig. 3) on the shaft I 3, and a key 36 in aligned keyways in the shaft and the hub portion effects the driving connection between them.

The right hub portion 2| (Fig. 3) and the shaft [3 are given a driving connection by a gib to the shaft by screws 46.

Two additional gib keys 4|, at 120 on centers from the key 38, are fitted in keyways 42 in the shaft and made fast by screws 43, each having a head 44 fitted tightly against the right end of the hub portion 2|, as shown in Fig. 3.

There is a clearance at 45, (Fig. 5) between the adjacent blade bases 23 of not portions 25 of the blades. There is a clearance of about .003"-between the ribs 21 and 2B and the adjacent portions of the shrouds, and a clearance of about .010" at the bottom of the notches 29 in the shrouds. suitable for a fan of 18" in diameter and are given to insure that the disclosure is complete, but notwith the intent of imposing corresponding limitations on the claims.

According to one mode of assembly,

assembly brought to approximately the position shown in Fig. 3. The right hub portion 2| is then forced home and made fast by the keys 3! and 4|.

The form of single inlet fan shown in Figs. '7 and 8 (Sheet 4) corresponds in every particular are like Hence, in view of the detailed description that has been given with re- These clearances are of the bases 23. In this position will have to be spect to the double inlet fan construction, it will be sufficient to add the corresponding reference numerals to Figs. 7 and 8 to avoid repetition.

According to the preferred procedure, the hub Portions and blades will be will be made from sheets. By weighting the blades and a slight amount of fitting, the assembly can readily be given dynamic balance, and

the constructiondescribed will-insm'e that the cast and the shrouds strength about ,25'% of chromium and about 12% assess:

blades are held in proper relation with respect to the shaft, both for driving and to prevent outward movement due to centrifugal force, and the shrouds will be maintained in proper relation to the blades while each blade and shroud will be For fans to be used in temperatures up to about 1600 F. an alloy of iron containing about of nickel has but sometimes the comchanged to meet particular conditions. It may be necessary to use an alloy that is inherently weaker in been found satisfactory,

temperatures up to 900 F. steel may beused.

After the parts have been finished they should be annealed at temperatures above the highest perience with these fans, and they have been followed carefully; and further research directed particularly to service in furnaces at temperatures from 1500 F. to well above 1650 F., have resulted in further improvements which make the fans still more valuable under extreme conditions. These improvements now represent the preferred construction.

The detail of the 11', between the 9. Each sector 7 blades against outward movement under centrifugal force. These pins, being arranged on a circle, conform to the dynamic balance necessary in the fan The machining pads 56 and the sector shaped flanges 51 are joined to the inner portions 5 by gently curving fillets 64, generally indicated by In order to provide metal and the inner ends of the openings 58,-bosses are provided adjacent to the sector and 10, the ribs being'relatively short and the ribs 89 relatively long. The latter are approximately as long asthe shrouds are wide, and the former are only about the depth of the slots in the shrouds.

Each shroud 5| is a ring provided with outwardly opening slots "II, twelve in number, to receive the side edges of the several blades as the adjacent portions of the shrouds are received between the ribs 89 and I8. vTh shrouds are of uniform thickness to about the depth of the slots 1i, and from there inwardly they are gradually thickened, as indicated at I2, to provide additional strength for resisting thebursting tendencies of centrifugalforce on the shroud as a 5 whole.

The flange 80 of each hub portion has an inner flat face 18 for contact with and bearing against the grouped faces 5'! of the blades. outwardly of this face 13, which is at right angles to the axis, each flange 60 has an inclined face" provided with twelve slots 15 to receive and hold the-machined faces 58 of the converging edges 55 of the inner portion 54 ofthe blades, While the slots are backed by a considerable thickness of flange metal, the inner portions are rounded at the corners 16 to avoid any abrupt change of, surface that might foster cracks. The flt between i the sides of the slots and the machined faces 58 is close and, together with the dowel pins 8 I, pro- 40 vides a strong driving and holding joint between the hubsand the blades. The adjacent surfaces being remote from the axis of rotation, minor accumulations of tolerances have less effect on the flt than with the construction shown in Figs. 3

and 6. I Each "hub portion 52 has a bore .11 to receive the shaft 53, to which it is keyed. The left hub portion 52 in Fig. 9 rests against the shoulder 18 v on the shaft, and the right hub portion in Fig. 9

is held against the blades by a large locking collar '19, made fast by a lock nut 80 and a lock washer 8| having one tab 82 fitting. in one of the key slots in the shaft 53, andotheitabs 88 and 88 bent into therespec'tive notches 85 and 88 in the 55 lock nut 80 and the locking collar 18.

The fan shaft is water cooled and is made of carbon steel. The hubs 52 are ofsome suitable alloy. ,The shaft and the'hubs, therefore, have different coefficients of expansion. The tend- 00 ency thus created to increase the clearance between the hub portions and the shaft as the fan is heated up is greatly augmented by the fact that the shaft is water cooled and the hubs are not. Bearing in mind that all of the fan is carried by the hubs ,on the-shaft and that, a

30. .inch fan wheel substantially as shown in',.

Figs. 9-13, will weigh on the order of 650 pounds,

it is a'pparentthat a slight eccentricity between/ the hub portions and the. shaft results in 7 enormous forces due to lack of dynamic balance.

To prevent this condition and to obtain and maintain dynamic balance, three or more keys or splines are used to effect a driving connection between the shaft and the hub portions.

2,885,887 7 3. In Figs. 9, 10, and 11, keys are shown, and they.

Integral keys or splines will be preferred by some to separate keys fitted in aligned keyways in the hub portions and shaft, and preferably the integral splines will be in one piece with the hub portions and broached with great accuracy to fit the keyways in the shaft.

The locking collar, .lock washer, and lock nut for making the hub members 82 fast on the shaft have a great advantage over the gib keys shown. in Figs. 3 and 'Lin providing greaterstrength due to they extended surface contact and also because the locking collars can be adjusted to allow .for the necessary expansion which may be calculated accuratelywithin reasonable limits. I a

As heretofore made in a 30-inch fan, the outer portions of the shrouds were .245.inch thick with an allowance of plusorminus .003, and the,

grooves 88 were .250 inch with an allowance of plus .003 minus .000. The inner edges of the shrouds were 1/. inch thick, and the corners were rounded on a inch radius.

The slots I5 in the flanges 88 of the hub portions were inch wide plus .005 minus .000,

and the inclined edges, at the machined faces 85 were .498 inch thick plus .002 minus 0.000. The sector shaped flanges 81 were 23 26'. The openings 58 were 1 inch in diameter reamed plus, .000 minus .002. The openings 88 in the flange 80 were the same, and all the openings were arranged on circles of an 8 inch diameter. The machined faces 58 extended to approximately 8 inches from the axis of rotation and were about /2 inch wide. The side faces of the sector shaped flanges 5'! were about /4 of an inch wide. I I f The outer surface of the flange 88 on the hub portion was about 28 inclined to the vertical..and the inner'face of the same flange was about so to .the vertical. The inside, diameter of the shrouds was 20 inches. There was thus provided ample inlet openings at each side somewhat inexcess of the discharge opening at the perimeter of the fan.

The slots 1| in the shrouds were 1% inches deep, or about 5 of the 5 inch radial width of the shrouds.

Adjacent sector shaped flanges 81 are spaced I by an angle 6 34'.

These and other clearances and dimensions. are given to insure complete disclosure for one size of fan that has been satisfactory in actual service, but they are-not intended to impose any limitations on the claims.

Accordingto one mode of assembly, the inner hub portion is in place on the shaft against the shoulder I8. The blades are assembled with the two shrouds and brought into position with the pins projecting from the hub flange 88 into the openings in the blades. The other hub flangeis then brought into place; the collar 18" is threaded on, the lockwasherslipped into place, the lock nut screwed up. and the tabs '88 and 88 bent over. 4 1

The single inlet fan embodying the characstrength for a long period to a great distance from the axis 01 01' the fan.

teristics of the double inlet fan shown in Figs. 9-13 is shown in Figs. 14-17 (Sheet 7). It corresponds to the double inlet fan in every particular, except that the blades are cut away at the right, as shown best by comparing Figs. 9 and 14, and the shroud i! at the right is wide enough to close the right side of the fan, leaving the entire inlet at the left.- Hence, in view of the detailed description that has been given with respect to, the double'inlet fan, it will be sufficient to add the corresponding numerals to Figs. 14-17.

Instead of using the dowel pin G l (shown in Figs. 9-14), some will prefer to fasten the blades 50 to the hub portions 52 by rings 86, as shown in Fig. 18,. fitted into circular grooves 81 in the hub flanges 60 and circular notches 88 in the blades as shown in Fig. 20. By this construction, of course it will be necessary to set the blades in a fixture for machining the notches 88 accurately, but the assembly is somewhat simplified.

A further alternative is shown in Fig. 19, where, instead of a separate ring 86 shown in Fig. 18,

the hub flange'iil is provided with an integral ring flange. 89. A reverse of that will be preferred by some,,and isshown in Figs. 21 and 22,

where the blades are provided with circular ribs 90 fitting in a circular groove ill in the hub flange 60.

According to the preferred construction, the hub portions, the blades, and the shrouds are all the blades, the two shrouds, and the two hub portions, respectively, identical. After the machining, the parts should be annealed at a temperature above the. highest to be expected in service in order to remove internal strains that might be released in service and throw the fan out of balance. By weighing the blades and a slight amount of fitting, readily given dynamic balance and the construction described will insure that balance in service as well as the necessary of service.

vThe purpose of the pins or rings for fastening the blades to the hubs is to make them secure, each at the same distance from the axis of rotation; in other words, to establish a datum line at which each of the blades centrifugal force.

the blades wedge shaped and the'hubs to correspond is to give the hubs a grip on the blades rotation asan of safety against a blade,

:1 blade, getting free on account of a break across 1 between two of the fastening pins or rings.

The slots in the hubs to receive the inner efiective drive between the hubs and the blades. The inclination of the hub, flanges provides the necessary inlet or intake, and in the improved construction the intake on the two sides. between the hub flanges and the shrouds gives an intake the discharge'at the perimeter area in excess of the maintenance of d is fastened and held' against outward individual movement due to or a portion of 1 under the conditions to cast from a suitable alloy and machined to make I the assembly can be be as much as that.

.alloys used lose a great ening the inner portion-that Each slot II in the shrouds 12 is of an inch wide, and the bottom is formed by a inch drill before the slotting. It is 1% and receives the corresponding portion of the blade between theribs 69 and 10, where it is 1 inches wide. This portion is also of an inch thick, only unavoidable manufacturing clearance being allowed.

Bearing in mind that the machined faces 56 on the inner portions of the blades are firmly and accurately held in place in the slots 15 of the hub flanges 60 to a diameter of 15 inches in a 30 inch fan, it will be apparent that the shrouds .are borne upon and driven by 12 blades accurately positioned in the open ended slots H. Being thus borne and driven without any actual blades, they are not only free ject only to centrifugal force.

According to one scheme of design, the'resultant of one-half the centrifugal force on each shroud should be assumed as applied to a radius at right angles to the diameter severing that hall from the other, and hence one-half of that re sultant force indicates the stress at each end of the said diameter, From this, it follows that the slots II should. be made as sha-llow as practical of the shrouds at the slots, for when a fan is working under extreme temperatures, on the order of 1600 to 1800" Fahrenheit, some of the deal of the normal tensile strength, and there is likelihood that centrifugal forcewill cause a creep or elongation in line with the slots which would change the clearances and cause an actual enlar ement of the diameter of the shroud. An empirical rule is that the slots should not be more-than one-third of the radial width of the shroud, but they need not necessarily It is fundamental that thickening the shroud throughout its radial dimension would not provide any greater strength, for the centrifugal force would increase in exact proportion to the thickening. Any increase might be had by thickis,- the radially inner portion-of the shroud, and theoretically the strength could be most advantageously'obtained by thickening at or adjacent to the inner periphery, but this would violate thecardinal principle that there should be no abrupt changes in section, and no corners. Hence, the tapered design shown in Figs. 9, 13, and 16 providing the flat inner face of the shroud at right angles to the axis of rotation and the inclined outer face from adjacent to the bottom of the slots H to the inner perimeter. This outer face need not necessarily be a straight line, but may be curved.

The shroud l5l at the wheel in Fig, 14 needs no thickening for the additional strength is provided by thesmaller opening in the shroud, resulting in the greater extent of metal radially.

' The particular relation between the outer portions of the blades and the shrouds permits the element of freedom while providing,ample support in driving. It also permits the blades to be made separate'from the hubs, thereby avoiding the complications'of cast- 1 .18, and by the scheme here disclosed the blades are secured to the hub portion to the shaft in a way that not only certainty against outward inches deep,

avoid undue weakening closed side of the single,

in expansion and contraction hub portion and through the' movement under centrifugal force, but also holds them in the correct line with respect to the slots in the shrouds and preserves them from the slight malpositioning that might occur due'to the ac- I cumulation of tolerances in a different construction. Of course, tolerances may accumulate in the structure shown, but they are very likely to be found by the assembly inspection," and corrected.

In connection with the construction shown in Figs. 3 to 8 inclusive, it has been found preferable to eliminate the taper in the bore 3| of the hub, portions 2 l and the corresponding taper 32 on the bases 23. v

I claim:

a 1. In a centrifugal fan, a, plurality of blades in circular arrangement about a common axis of rotation with their inner portions converging inwardly toward said axis and their outer portions diverging outwardly from said axis, a shaft, hub members grasping the blades by their inner end portions to bindthem fast to the shaft, and shrouds carried by the blades, one at each side of the circular arrangement of blades, each shroud having outwardly opening slots in which grooved side edges of the blades are received with freedom of the blades and shrouds to have relative movement in expanding and contracting.

2. In a centrifugal fan, a plurality of blades in circular arrangement about a common axis of rotation with their inner portions converging inwardly toward said axis and their outer portions diverging outwardly from said axis, hub members grasping the blades by their inner end portions to hold the blades against individual bodily movement outwardly due to centrifugal force, and. shrouds carried by the blades, one at each side of the circular arrangement of blades and interlocked with the several side edges of the blades by joints preventing axial separation of the blades and shrouds and providing individual freedom of the blades and shrouds to have relative movement in expanding and contracting.

3. In a centrifugal fan, a plurality of blades, in circular arrangement about a common axis of rotation with their inner portions converging inwardly toward said axis and their outer' portions diverging outwardly from said axis, means to hold the blades by their inner end portions against individual bodily movement outwardly due to centrifugal force, and shrouds carried by the blades, one at each side of the circular arrangement of blades, each shroud having outwardly opening slots in which grooved side edges of the blades are received with freedom of the blades and shrouds to have relative movement in, expanding and contracting.

i 4. In a centrifugal fan, a plurality of blades.

in circular arrangement about a common axis of rotation with their inner portions converging inwardly toward said axis and their outer portions diverging outwardly from said axis, means to hold the blades by their inner end portions against individual bodilyv movement outwardly due to centrifugal force, and shrouds carried by the blades,one at each side of the circular arrangement of blades, each shroud having slots, in which the side edges of the blades are engaged" with freedom of the blades and shrouds to'have relative movement in expanding and contracting, and each blade having a rib at each side edge in circular arrangement about a common axis of rotation with their inner portions converging inwardly toward said axis and their outer portions diverging outwardly from said axis, means to hold the blades by their inner end portions against individual bodily movement outwardly due to centrifugal force, and shrouds .carried by the blades, one at each side of the circular arrangement of blades and interlocked'with the several side edges of the blades by joints preventing axial separation of the, blades and shrouds and providing individual freedom of the blades and shrouds to have relative movement in ex-.

panding and contracting. g

6. In a centrifugal fan, a plurality of blades in circular arrangement about acommon axis of rotation with their inner portions converging inwardly toward said axis and their outer portions diverging outwardly from said axis, said inner portions being enlarged axially, a shaft, hub

, members securing said, enlarged inner portions to the shaft, and annular shrouds each having an outwardly open slot for each blade interlocked with a groove in the adjacent blade whereby the shrouds are maintained connected to the blades and axial separation of the blades and shrouds is prevented by the interlocked grooves and'slots.

7. In a centrifugal fan, a plurality of blades in circular arangement about a common axis of rotation with' their inner portions converging inwardly toward said axis and their outer portions diverging outwardly from, said axis, said inner portions being enlarged axially, a shaft, hub members securing said enlargeddnner portions to the shaft, and annular shrouds each having a'slot for each bladeopen at the outer periphery of the shroud and terminating short of its inner periphery interlocked with a groove in the adjacent blade whereby the shrouds are maintained connected to the blades and mounted thereon.

'8. In a centrifugal fan, a plurality of blades in circular arrangement about a common axisv of rotation with their inner portions converging inwardly toward saidaxis and their outer portions diverging outwardly from said axis, said inner portions being enlarged axially, a shaft, hub

members securing said enlarged inner portions to the shaft, each blade having at its side edges inner and outer ribs providing grooves between the ribs, and annular shrouds each having a slot for each lblade receiving said grooves to interlock the shrouds, with the blades and maintain the shrouds mounted on the blades.

9. In a centrifugal fan, ashaft, a plurality of generally radially extending blades mounted on the shaft and each havinga side edge thickened and oppositely. grooved, and an annular shroud having a slot for. each adjacent pair of blade grooves open to the outer periphery of the shroud and terminating short of the inner periphery,

each of said slots and the adjacent pair of grooves being interfitted to mount the shroud on the plurality of blades.

cent pair of blade grooves open to the outer pcoverlapping the adjacent slot in the shroud for preventing relative axial movement of the blades and shrouds. v 7

5. In a centrifugal fan,aplurality of blades ri-phery of the shroud and terminating short of the inner periphery, each of said slots and the adjacent pair of grooves being interfltted to mount the pair of shrouds on the plurality of blades,

g 11. In a centrifugal fan, an annular shroud and shrouds carried common axis of rotation to hold the assembly of blades and shroudtogether.

12. In a centrifugal fan, a shaft, hub portions on the shaft, a plurality of blades in circular arrangement about said shaft with their outer portions diverging outwardly from the axis and their inner portions converging inwardly toward the.

axis and clamped between the said hub portions, by the blades, one at each side of the circular arrangement of blades and interlocked with the several side edge portions of the blades by joints preventing axial separation of the blades and shrouds and providing clearance between the blades and shrouds for individual freedom of the blades and shrouds to have relative movement in expanding and contracting.

13. In a centrifugal fan, a shaft, a plurality of blades in circular arrangement about said shaft with their inner portions converging inwardly toward the shaft and their outer portions diverging outwardly away from the shaft, hub members sleeved over the shaft having flanges grasping said inner portions with clearance for expansion and contraction with respect to said inner portions, but holding them against radially outward movement under centrifugal force and against rotary movement relative to the shaft, and shrouds carried by the blades, one at each side of the circular arrangement of blades and interlocked with the several side edge portions of the blades by joints preventing axial separation of the blades and shrouds and providing clearance between the blades and shrouds for individual freedom, of the blades and shrouds to have relative movement in expanding and contracting.

14. In a centrifugal fan, a plurality of blades in circular arrangement about a common axis- .of rotation with their inner portions converging inwardly toward said axis and their outer por tions diverging outwardly from said axis, means to hold the blades by their inner portions against individual movement outwardly due to centrifugal force, and shrouds carried by the blades, one at each side of the circular arrangement of blades and interlocked with the several side edges of the blades by joints preventing axial separation; of the blades and shrouds and providing individual freedom of the blades and shrouds to have relative movement in expanding and contracting, said shrouds being thickened toward the inner periphery.

15. In a centrifugal fan, a plurality of blades in circular arrangement about a. common axis of rotation with their inner portions converging inwardly toward saidaxis and their outer portions diverging outwardly from said axis, means to hold the blades by their inner portions against individual movement outwardly due to centrifugal force, and shrouds carried by the blades, one at each side of the circular arrangement of blades and interlocked with the several. side edges of the blades .by joints preventing axial separation of the blades and shrouds and providing individual freedom of the blades and shrouds to have relative movement in expanding and contracting, said trifugal force, and shrouds carried by the blades,

one 'at each. side of the circular arrangement of blades and interlocked with the several side edges of the blades by joint preventing axial separation of the blades and shrouds and-providing individual freedom of the blades and shrouds to have relative movemen tracting. V

17. In a centrifugal fan, a plurality of blades in circular arrangement about a common axis of rotation with inner portions converging inwardly toward said axis and outerportions diverging outwardly away from said axis, said inner portions having inwardly diverging side edges forming axial enlargements, inclined hub portions grasping the diverging side 'edges of the inner portions of the blades to hold them against individual bodily movement outwardly due to centrifugal force, and shrouds carried by the blades, one at each side of the circular arrangement of blades and interlocked with the several side edges of the blade by joints preventing axial separation of the blades and shrouds and providing individual freedom to have relative movement in expanding and contracting.

18. In a centrifugal fan, a plurality of blades in circular arrangement about a common axis of rotation with inner portions converging inwardly toward said axis and outer portions diverging outwardly away from said axis, said inner portions having inwardly diverging side edges form-' dividual freedom of the blades and shrouds to .freedom of the blades and have relative movementin expanding and con-' tracting, the inner peripheries of theshrouds' being spaced from the adjacent hub portions suf- J ficiently to provide an intake in excess of the peripheral discharge.

19. In a centrifugal fan, a plurality of blades in circular arrangement about a common axis of rotation with enlarged inner portions convergaxis and relatively wide outer portions diverging movement outwardly due to centrifugal force; and shrouds carried by the blades, one at each side of the circular arrangement of blades and interlocked with the several side edges of the blades by joints preventing axial separation of the blades and shrouds and providing individual tive movement in expanding and contracting.

20. Ina centrifugal fan,

in expanding and con- 1 of the blades and shrouds outwardly away from said axis, means to hold the blades by their en- 'larged inner portions against individual bodily shrouds to have rela-" a plurality ofblades 2,aso,sa7 a 7 in circular arrangement about a common axis of rotation with enlarged inner portions converging inwardly toward said axis and relatively wide outer portions diverging outwardly away from said axis, hub members interlocked with the enlarged inner portions of the blades at auniform distance from the axis of rotation to hold them against individual bodily' movement outwardly under centrifugal force and against rotary movement independent of the hub members, and shrouds carried by the blades, one at each side of the circular arrangement of the blades and interlocked with the several side edges of the blades by Joints preventing axial separation of the blades and shrouds and providing individual freedom of the blades and shrouds 'to have relative movement in expanding and contracting.

' CARL NYGREN. 

